…e if not set

This name is stored in the tarball, and applications like '7z'
extract under that name. Without a valid extension, it gets lost
a bit after that. So help it out a bit.

Python switched to PAX-format for tarballs by default. OpenTTD
supports ustar-format; although that should mean it should be
compatible with PAX-format too, it is mostly wasting bytes.

Otherwise the API can think a package exists, but it really doesn't.
As git doesn't track folders, only files, we need to do some manual
cleanup.

By keeping a reference around to the original edited package, we
can commit it after a reload safely.